DOCSLIB.ORG

Mineral Assemblages in Granitoid Rocks: Melt : Biotite Reaction in The

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Mineral Assemblages in Granitoid Rocks: Melt : Biotite Reaction in The American Mi ner al o gist, Volume72, pages 863-878, 1987 Evolutionof magmaticAFM mineral assemblagesin granitoid rocks: The hornblende* melt : biotite reaction in the Libertv Hill pluton, South Carolina J. Ar,nxaNDER SPEER* OrogenicStudies Laboratory, Department of GeologicalSciences, Virginia Polytechnic Institute and StateUniversity, Blacksburg,Virginia 24061, U.S.A. AssrRAcr The Liberty Hill pluton comprisesa central, coarse-grainededenite + biotite granitoid faciesgrading to a biotite, pargasite + biotite, or muscovite * biotite granitoid marginal facies.The replacementof amphibole by biotite, mineral compositions, and "liquid" vari- ation diagrams for the Liberty Hill help determine the AFM mineral-crystallization re- actions in the Liberty Hill pluton. These reactions evolved from liquid : amphibole to liquid : biotite with an intervening liquid + amphibole : biotite reaction resulting from either (l) movement along the amphibole-biotite liquidus boundary from the even, liq- uid: amphibole * biotite, to the odd, liquid + amphibole : biotite, crystallization reaction with decreasingtemperatures or (2) movement of the liquid composition from the amphibole field into the biotite field. The liquid + amphibole : biotite reaction involved additional phases;the full reaction may have taken the form liquid I + amphi- bole*ilmenite:biotite+qtrarlz+anorthite+K-feldspar+titanite+magnetite+ liquid 2, where the liquid is the interstitial melt. The extended crystallization history to lower temperaturesand higher water activities at the margins of the pluton allowed the reaction to exhaust the amphibole before the liquid; the subsequentliquid : biotite crys- tallization reaction produced the biotite granitoid facies. Locally, muscovite crystallized accordingto the reaction liquid : muscovite + biotite, producing the muscovite + biotite facies. The pluton is intruded by a finer-grained biotite granitoid believed to be derived from interstitial melt of the coarser-grainedgranitoids. This derivation explains why bio- tite is the only AFM mineral in the finer-grained granitoids and why biotites from all Liberty Hill granitoids are generally similar in composition. The averageKo value l(XBJe/XB;)/(W;/Xf"b')lis 1.04 for coexisting Hbl and Bt. This K" is higher than the 0.69-0.93 normally observed in igneousrocks, but equal to values for specificinstances of biotite replacing amphibole in the Peruvian Coastal batholith. Com- bined with the results obtained from the contact aureole, the central granitoids preserve conditions of 725"C,P,oor E 4.5 kbar, Po",oE 0.5 P,"o,,andfo, - 10-15,slightly more oxidizing than the NNO solid buffer. Marginal granitoids yield conditions of 647"C, Po,,or P,.^,, andfo, I 10-16,suggesting a more prolonged reaction history. INrnonucrroN ciesoverlap thoseofthe centralgranitoids, arguing against Many of the late Paleozoic granitoid plutons of the significant differentiation (Speeret al., unpub. ms.). The southernAppalachians are composite bodies with coarse- marginal facies do show minor wall rock-magma inter- grained amphibole + biotite and biotite varietal facies action that affectedsome trace-elementand oxygen-iso- (Speeret al., 1980). From field relations, thesefacies ap- tope compositions(Wenner and Speer,1986). An alter- pear closelyrelated, and multiple intrusion or differentia- native explanation for the mineralogical relation between tion comesto mind as an explanation for the relationship. the central and marginal facies is suggestedby the wide- In the Liberty Hill pluton, the coarse-grainedcentral am- spreadtexture of biotite replacing amphibole. phibole + biotite granitoids grade imperceptibly into Understanding the mineral assemblagesand composi- marginal biotite granitoids, seeminglyruling out multiple tions in igneousrocks requires linking them to the evolv- intrusions. The compositions of the marginal biotite fa- ing conditions and compositions of the interstitial melt during crystallization. This is a well-developed area of gabbroic * Present address:Department of Marine, Earth and Atmo- investigation for rocks, but much less so for spheric Sciences,Box 8208, North Carolina State University, granitoid rocks. Recently, Abbott and Clarke (1979) and Raleigh,North Carolina27695-8208, U.S.A. Abbott (1981, 1985) have given the sequenceofAFM 0003404x/87/09 I 0-0863$02.00 863 864 SPEER:EVOLUTION OF MAGMATIC AFM ASSEMBLAGES IN GRANITOID ROCKS crystallization reactionsin granitoids in more detail than given in Tables 1 to 3. Mineral formulas and componentswere Bowen's(1928) reaction series. These have beenused in calculatedusing the computer program suPERrncer-ofRucklidge program stoichiometric interpreting the crystallization reactions in strongly per- (1971). The also calculatedan assumed amount of water and added it to the oxide weight percentages aluminous granitoids, such as the cordierite-bearing for the hydrous minerals. Mineral abbreviations in the text, ta- pluton, South Carolina (Speer,198 1b). Their CloudsCreek bles, and figuresare those recommendedby The American Min- use is extended here to the metaluminous Liberty Hill eralogist(ketz, 1983). pluton, South Carolina, in order to understand the evo- lution of amphibole + biotite, biotite, and muscovite + Amphibole biotite granitoids. Amphibole occursas euhedralto subhedralprismatic crystals up to 0.5 cm long. They are pleochroic dark yellow green to Gnolocrc sETTTNG moderate blue green and are locally twinned on (100). Micro- The Liberty Hill pluton is roughly elliptical, covering probe analyses(App. 1, selectedanalyses in Table l) show that 360 km'zin Kershaw, l,ancaster, and Fairfield Counties, the amphiboles in the central granitoids are ferro-edenitesand north-central South Carolina. The Liberty Hill pluton ferro-edenitic hornblendes(Fig.2a), hereafterreferred to as fer- comprises severaltexturally and mineralogically distinct ro-edenites.These ferro-edeniteshave a narrow compositional Fe/(Fe + Mg) near 0.6 and a Si content in the facies(Fig. 1). The predominant faciesis a coarse-grained range with an half-unit-cell formula of 6.56 to 6.85 atoms per 24 anions. The ferro-edenite + biotite granitoid occupying the center of F and Cl contents rangebetween 0.08 and 0.22 molo/oF/(OH + pluton. pargasite the Coarse-grainedbiotite, ferroan + F + Cl) and between0.005 and 0.03 mo10/oCV(OH + F + CD, biotite, and muscovite * biotite granitoids occur along respectively.Amphiboles in granitoids of the northeast corner the northern and easternborders ofthe pluton and have of the pluton have thin, discontinuousaluminous rims of ferroan gradational contactswith the central ferro-edenite * bio- pargasite(Fig. 2B). Thesealuminous rims are lessthan 0.01 mm tite granitoids. This reversezoning of the mineral facies thick and are only locally visible, where there is a color difer- is believed to result from accumulation of magma with a ence. According to graphical representationsof Doolan et al. greater percentageof evolved, interstitial melt near the (1978)and Thompson(1981), the substitutionin the aluminous margin as a result of the pluton's emplacementas well as rims is primarily a tschermakite [AlrMg 'Si-'] + edenite to form pargasite. a minor amount of contamination from the wall rocks [NaAlSi-,] substitution Many amphiboles are intergrown with biotite, but generally (Wenner and Speer, 1986). There are severalyounger fa- the order of crystallization is uncertain. Where textures are un- pluton cies in the Liberty Hill that intrude the coarse- ambiguous,the amphiboles are partially (Fig. 3a) or completely grained granitoids as dikes or plugs up to I km2 in area. (Fig. 3b) replaced by biotite. In what is interpreted as a later The most prominent are fine- to medium-grained biotite reaction texture, amphiboles can be replacedby chlorite + epi- granitoids in the west-centralpart ofthe pluton (Fig. 1), dote + plagioclase.Scattered throughout the pluton are amphi- which are believed to have differentiated from the coarse- boles with clinopyroxene inclusions (Fig. 3c). The amphibole grained facies. adjacent to these pyroxenes is pale green actinolite that is dis- The contact aureole of the pluton was described by continuously zoned to ferro-edenite at the rim, comparable in pluton (Fig. Speer(198 I a). The pelitic assemblagein the country rock, composition to amphiboles elsewherein the 2b). muscovite + chlorite + albite * epidote + quartz + Biotite magnetite + ilmenite, changesin responseto prograde Greenish-blackbiotite is a ubiquitous mafic phasein the Lib- pluton. metamorphism on approachingthe The following erty Hill pluton, forming up to 5 modal percent of the rock. isograds are encountered:porphyroblastic magnetite in, Biotite occursinterstitially to feldsparsand quartz, replacingam- epidote + albite out, biotite + cordierite in, chlorite out, phibole, and as inclusions in leucocratic minerals. Individual K-feldspar in, and muscovite or magnetite out. Several flakesare up to 5 mm across.Biotite is pleochroic grayish orange additional metamorphic minerals appearin the xenoliths: to greenishblack in thin section. garnet, orthopyroxene, andalusite, sillimanite, and fi- Microprobe analyses(App. l, selectedanalyses in Table 2) brolite. It was concluded that the pluton was emplaced show that biotite compositions from the granitoids fall approx- phlogopite at a depth correspondingto 4.5-kbar pressure.The mag- imately midway between and annite with an inter- The range of molar Fel(Fe + Mg) is small ma was relatively dry, and the xenoliths yield estimated mediate Al
Load more

Recommended publications
  • The Oxidation Ratio of Iron in Coexisting Biotite And
    1423 The Canadian Mineralo gist Vol.37. pp. 1423-1429(1999\ THE OXIDATIONRATIO OF IRON IN COEXISTINGBIOTITE AND HORNBLENDEFROM GRANITICAND METAMORPHICROCKS: THE ROLE OF P, T AND f(O2) NADINES. BORODINA, GERMAN B. FERSHTATER$erro SERGEI L. VOTYAKOV Institute of Geology and Geochemistry, RussianAcademy of Sciences,Pochtoty per., 7, Eknterinburg, 620151, Russia Assrnecr Previously published and new data on the composition of coexisting biotite and homblende from granitic and metamorphic rocks show that the degree of iron oxidation, R [= Fe3*/(Fe2*+ Fe3*)], is different in these two minerals; the R of hornblende is greater. Granulite-facies minerals have the greatest difference in R, whereas in granitic rocks, those minerals show the least difference The oxidation of biotite and hornblende under high-level conditions is accompaniedby the crystallization of magnet- ite, and newly formed oxidized mafic minerals have a lower Fe/(Fe + Mg) and R than the original ones. Under mesozonal and catazonalconditions, the increasein pressureprevents the formation of magnetite, and oxidation is accompaniedby a significant increase in R; these changes in the chemical composition of hornblende are supplementedby an increase in Al. Since the Al content of homblende is known to be an indicator of pressure, such a correlation of R and Fer+ content with aluminum content points to an increaseof theseparameters with a rise of pressure Keywords:biotite, hornblende,oxidation ratio, granitic rocks, metamorphic rocks, epizonal plutons, mesozonalplutons , cat^7'onal plutons. Sorravarnr, Les donn6esnouvelles et celles tirde de la litt6rature portant sur 1acomposition de la biotite et celle de la hornblendecoexistante des roches granitiques et m6tamorphiquesmontrent qui le degrd d'oxydation du fer, R [= Fe3*/(Fe2*+ Fe3+)],est diffdrent dans ces deux mindraux.
    [Show full text]
  • Igneous Garnet and Amphibole Fractionation in the Roots of Island Arcs: Experimental Constraints on Andesitic Liquids
    CORE Metadata, citation and similar papers at core.ac.uk Provided by Serveur académique lausannois Contrib Mineral Petrol (2009) 157:541–558 DOI 10.1007/s00410-008-0351-8 ORIGINAL PAPER Igneous garnet and amphibole fractionation in the roots of island arcs: experimental constraints on andesitic liquids Raquel Alonso-Perez Æ Othmar Mu¨ntener Æ Peter Ulmer Received: 23 January 2008 / Accepted: 6 October 2008 / Published online: 30 October 2008 Ó Springer-Verlag 2008 Abstract To evaluate the role of garnet and amphibole for ‘slab melting’, or dehydration melting in the deep arc. fractionation at conditions relevant for the crystallization of Garnet fractionation, either in the deep crust via formation magmas in the roots of island arcs, a series of experiments of garnet gabbros, or in the upper mantle via formation of were performed on a synthetic andesite at conditions garnet pyroxenites remains an important alternative, ranging from 0.8 to 1.2 GPa, 800–1,000°C and variable despite the rare occurrence of magmatic garnet in volcanic H2O contents. At water undersaturated conditions and fO2 rocks. established around QFM, garnet has a wide stability field. At 1.2 GPa garnet ? amphibole are the high-temperature Keywords Experimental petrology Á Hydrous andesite liquidus phases followed by plagioclase at lower tempera- liquids Á High-pressure crystallization Á Amphibole Á ture. Clinopyroxene reaches its maximal stability at H2O- Garnet fractionation contents B9 wt% at 950°C and is replaced by amphibole at lower temperature. The slopes of the plagioclase-in boundaries are moderately negative in T-XH2O space. At Introduction 0.8 GPa, garnet is stable at magmatic H2O contents exceeding 8 wt% and is replaced by spinel at decreasing Major and trace element similarities between estimates of dissolved H2O.
    [Show full text]
  • Reworked Restite Enclave
    Reworked restite enclave: Petrographic and mineralogical constraints from the Tongshanling intrusion, Nanling Range, South China Xu-Dong Huang, Jian-Jun Lu, Stanislas Sizaret, Ru-Cheng Wang, Jin-Wei Wu, Dong-Sheng Ma To cite this version: Xu-Dong Huang, Jian-Jun Lu, Stanislas Sizaret, Ru-Cheng Wang, Jin-Wei Wu, et al.. Re- worked restite enclave: Petrographic and mineralogical constraints from the Tongshanling intru- sion, Nanling Range, South China. Journal of Asian Earth Sciences, Elsevier, 2018, 166, pp.1-18. 10.1016/j.jseaes.2018.07.001. insu-01856863 HAL Id: insu-01856863 https://hal-insu.archives-ouvertes.fr/insu-01856863 Submitted on 10 Dec 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Reworked restite enclave: Petrographic and mineralogical constraints from the Tongshanling intrusion, Nanling Range, South China Xu-DongHuangab Jian-JunLua StanislasSizaretb Ru-ChengWanga Jin-WeiWua Dong-ShengMaa A : State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China B : Institut des Sciences de la Terre d’Orléans, UMR 7327-CNRS/Université d’Orléans/BRGM, Orléans 45071, France Abstract Microgranular enclaves, which can provide important petrogenetic indications for the host granitoids, are commonly observed in the Middle-Late Jurassic Cu-Pb-Zn-bearing granodiorites in the Nanling Range of South China.
    [Show full text]
  • Mineralogy and Paragenesis of Amphiboles from Gibson Peak Pluton
    THE AIVIERICAN MINERALOGIST, VOL. 49, SEPTEMBER-OCTOBER. 1964 MINERALOGY AND PARAGENESIS OF AMPHIBOLES FROM GIBSON PEAK PLUTON. NORTHERN CALIFORNIA PBrBn W. Lrelrlx, U. S. Geotogi,calSurvey, Denaer,Colorad,o. Ansrnacr Ixrnooucrrow Gibson Peak pluton, a 3-squaremile compositeintrusion in the Trin- itv Aips of northern california, is particularly suitablefor investigation of relations between amphibole paragenesisand igneouscrystallization becauseseveral distinctive amphiboles are important constituents of geneticallyrelated rocks that range from gabbro to trondhjemitic tona- lite. This paper describesthe sequenceof amphibole crystallization in difierent parts of the intrusion and reiates the compositionsof three newly analyzedamphiboles to crystallizationsequence and composition of the enclosingrock. The main conclusionis that compositionsof the investigatedamphiboles are as dependenton time of crystallizationwithin their respectiverocks as on bulk rock composition. Pnrnocn.q.pnrcrNtrnpnBTATroN oF THE Alrpnrsolr panecnNpsrs The generalstructural and petrologicfeatures of Gibson peak pluton are describedelsewhere (Lipman, 1963),and onl1-relations bearing on the origin of the amphibolesare summarizedhere. The pluton is com- posite,and five discreteintrusive units have beenrecognized on the basis of field relations.rn order of intrusion theseare hypersthene-hornblende gabbro, (augite-)hornblendegabbro, hornblende diorite, porphyritic quartz-bearingdiorite, and trondhjemitic biotite tonalite. All units show intrusive contacts with the preceding rocks, are petrographically dis- tinctive, and contain at least one amphibole. An interpretation of th" peak complex paragenesisof the Gibson amphiboles,based mainly on the textural featuresdescribed below, is presentedin Fig. 1. The evi- denceis clear orr the occurrenceof the indicated reactions,but the rela- 1321 PETER W. LIPMAN I I I F I I F I 1 I I cd d l :d d9 z z t.i r F-] {Fl z z.zt- z .=l il.
    [Show full text]
  • Petrogenesis of Slab-Derived Trondhjemite-Tonalite-Dacite/ Adakite Magmas M
    Transactions of the Royal Society of Edinburgh: Earth Sciences, 87, 205-215, 1996 Petrogenesis of slab-derived trondhjemite-tonalite-dacite/ adakite magmas M. S. Drummond, M. J. Defant and P. K. Kepezhinskas ABSTRACT: The prospect of partial melting of the subducted oceanic crust to produce arc magmatism has been debated for over 30 years. Debate has centred on the physical conditions of slab melting and the lack of a definitive, unambiguous geochemical signature and petrogenetic process. Experimental partial melting data for basalt over a wide range of pressures (1-32 kbar) and temperatures (700-1150=C) have shown that melt compositions are primarily trondhjemite- tonalite-dacite (TTD). High-Al (> 15% A12O3 at the 70% SiO2 level) TTD melts are produced by high-pressure 015 kbar) partial melting of basalt, leaving a restite assemblage of garnet + clinopyroxe'ne ± hornblende. A specific Cenozoic high-Al TTD (adakite) contains lower Y, Yb and Sc and higher Sr, Sr/Y, La'/Yb and.Zr/Sm relative to other TTD types and is interpreted to represent a slab melt under garnet amphibolite to eclogite conditions. High-Al TTD with an adakite-like geochemical character is prevalent in the Archean as the result of a higher geotherm that facilitated slab melting. Cenozoic adakite localities are commonly associated with the subduction of young (<25Ma), hot oceanic crust, which may provide a slab geotherm (*9-10=C km"1) conducive for slab dehydration melting. Viable alternative or supporting tectonic effects that may enhance slab melting include highly oblique convergence and resultant high shear stresses and incipient subduction into a pristine hot mantle wedge.
    [Show full text]
  • Alkalic Rocks of Iron Hill Gunnison County, Colorado
    If yon do not need this publication after it has served your purpose, please return it to the Geological Survey, using the official mailing label at the end UNITED STATES DEPARTMENT OF THE INTERIOR ALKALIC ROCKS OF IRON HILL GUNNISON COUNTY, COLORADO GEOLOGICAL SURVEY PROFESSIONAL PAPER 197-A UNITED STATES DEPARTMENT OF THE INTERIOR Harold L. Ickes, Secretary GEOLOGICAL SURVEY W. C. Mendenhall, Director Professional Paper 197-A ALKALIC ROCKS OF IRON HILL GUNNISON COUNTY, COLORADO BY ESPER S. LARSEN Shorter contributions to general geology, 1941 (Pages 1-64) UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON : 1942 For sale by the Superintendent of Documents, Washington, D. C. ......... Price 40 cents CONTENTS Page Preface, by G. F. Loughlin_________________________ v Other dike rocks_______________-____________________ 29 Abstract____"_--__-___--__________________________ 1 Augite syenite and shonkinite ____.__--___--__--__ 29 Introduction. ______________________________________ 1 Olivine gabbro. ________________________________ 30 Location and topography. _______________________ 1 Carbonate veins_________----__---------__--_---___- 31 Field work and acknowledgments.________________ 2 Character __ __________________________________ 31 Geology of the surrounding area__________________ 2 Origin _______ _ ____ _ __ _.. __ __. ___ .__. 31 Age of the Iron Hill stock_____________________ 2 Hydrothermal processes- ______--_-___-_---_--__-___- 31 General geology of the Iron Hill stock _____________ 3 The hydrothermal products. _____________________
    [Show full text]
  • A Systematic Nomenclature for Metamorphic Rocks
    A systematic nomenclature for metamorphic rocks: 1. HOW TO NAME A METAMORPHIC ROCK Recommendations by the IUGS Subcommission on the Systematics of Metamorphic Rocks: Web version 1/4/04. Rolf Schmid1, Douglas Fettes2, Ben Harte3, Eleutheria Davis4, Jacqueline Desmons5, Hans- Joachim Meyer-Marsilius† and Jaakko Siivola6 1 Institut für Mineralogie und Petrographie, ETH-Centre, CH-8092, Zürich, Switzerland, [email protected] 2 British Geological Survey, Murchison House, West Mains Road, Edinburgh, United Kingdom, [email protected] 3 Grant Institute of Geology, Edinburgh, United Kingdom, [email protected] 4 Patission 339A, 11144 Athens, Greece 5 3, rue de Houdemont 54500, Vandoeuvre-lès-Nancy, France, [email protected] 6 Tasakalliontie 12c, 02760 Espoo, Finland ABSTRACT The usage of some common terms in metamorphic petrology has developed differently in different countries and a range of specialised rock names have been applied locally. The Subcommission on the Systematics of Metamorphic Rocks (SCMR) aims to provide systematic schemes for terminology and rock definitions that are widely acceptable and suitable for international use. This first paper explains the basic classification scheme for common metamorphic rocks proposed by the SCMR, and lays out the general principles which were used by the SCMR when defining terms for metamorphic rocks, their features, conditions of formation and processes. Subsequent papers discuss and present more detailed terminology for particular metamorphic rock groups and processes. The SCMR recognises the very wide usage of some rock names (for example, amphibolite, marble, hornfels) and the existence of many name sets related to specific types of metamorphism (for example, high P/T rocks, migmatites, impactites).
    [Show full text]
  • Rock and Mineral Identification for Engineers
    Rock and Mineral Identification for Engineers November 1991 r~ u.s. Department of Transportation Federal Highway Administration acid bottle 8 granite ~~_k_nife _) v / muscovite 8 magnify~in_g . lens~ 0 09<2) Some common rocks, minerals, and identification aids (see text). Rock And Mineral Identification for Engineers TABLE OF CONTENTS Introduction ................................................................................ 1 Minerals ...................................................................................... 2 Rocks ........................................................................................... 6 Mineral Identification Procedure ............................................ 8 Rock Identification Procedure ............................................... 22 Engineering Properties of Rock Types ................................. 42 Summary ................................................................................... 49 Appendix: References ............................................................. 50 FIGURES 1. Moh's Hardness Scale ......................................................... 10 2. The Mineral Chert ............................................................... 16 3. The Mineral Quartz ............................................................. 16 4. The Mineral Plagioclase ...................................................... 17 5. The Minerals Orthoclase ..................................................... 17 6. The Mineral Hornblende ...................................................
    [Show full text]
  • Highly Aluminous Hornblende from Low-Pressure Metacarbonates And
    American Mineralogist, Volume 76, pages 1002-1017, 1991 Highly aluminous hornblendefrom low-pressuremetacarbonates and a preliminary thermodynamicmodel for the Al content of calcic amphibole Ar-rnnr Lfcrn, JoHN M. Frnnv Department of Earth and Planetary Sciences,The Johns Hopkins University, Baltimore, Maryland 21218, U.S.A. Ansrucr Calcic amphiboles in carbonate rocks at the same metamorphic grade from the Waits River Formation, northern Vermont, contain 2.29-19.06wto/o AlrO, (0.38-3.30Al atoms per formula unit, pfu). These Al-rich amphibole samplesare among the most aluminous examples of hornblende ever analyzed. The amphibole-bearing metacarbonatesare in- terbedded with andalusite-bearingpelitic schists and therefore crystallized at P < 3800 bars. Theseresults demonstrate that factors in addition to pressuremust control Al content in hornblende. We have identified temperature,mineral assemblage,mineral composition, and rock chemistry [especiallyFe/(Fe + Mg)] as other important factors. To explore semiquantitatively the dependenceof the Al content of calcic amphibole on P, T, and coexisting mineral assemblage,a simple thermodynamic model was developed for mineral equilibria involving tremolite-tschermakite ([CarMgrSi'O'r(OH)r]- [CarMg.AloSi6Orr(OH)r])amphibole solutions. The model uses the thermodynamic data base of Berman (1988), with the addition of new values for standard-stateenthalpy and entropy for pure end-member tschermakite derived from experimental and field data on the Al content in tremolite coexisting with diopside, anorthite, and quartz. Calculated phase equilibria lead to three conclusions:(l) At a specifiedP and T, the Al content of calcic amphibole is strongly dependenton the coexisting mineral assemblage.(2) No uni- versal relationship exists between the Al content of amphibole and P.
    [Show full text]
  • Description of Map Units
    GEOLOGIC MAP OF THE LATIR VOLCANIC FIELD AND ADJACENT AREAS, NORTHERN NEW MEXICO By Peter W. Lipman and John C. Reed, Jr. 1989 DESCRIPTION OF MAP UNITS [Ages for Tertiary igneous rocks are based on potassium-argon (K-Ar) and fission-track (F-T) determinations by H. H. Mehnert and C. W. Naeser (Lipman and others, 1986), except where otherwise noted. Dates on Proterozoic igneous rocks are uranium-lead (U-Pb) determinations on zircon by S. A. Bowring (Bowring and others, 1984, and oral commun., 1985). Volcanic and plutonic rock names are in accord with the IUGS classification system, except that a few volcanic names (such as quartz latite) are used as defined by Lipman (1975) following historic regional usage. The Tertiary igneous rocks, other than the peralkaline rhyolites associated with the Questa caldera, constitute a high-K subalkaline suite similar to those of other Tertiary volcanic fields in the southern Rocky Mountains, but the modifiers called for by some classification schemes have been dropped for brevity: thus, a unit is called andesite, rather than alkali andesite or high-K andesite. Because many units were mapped on the basis of compositional affinities, map symbols were selected to emphasize composition more than geographic identifier: thus, all andesite symbols start with Ta; all quartz latites with Tq, and so forth.] SURFICIAL DEPOSITS ds Mine dumps (Holocene)—In and adjacent to the inactive open pit operation of Union Molycorp. Consist of angular blocks and finer debris, mainly from the Sulphur Gulch pluton Qal Alluvium (Holocene)—Silt, sand, gravel, and peaty material in valley bottoms.
    [Show full text]
  • Metamorphism and the Origin of Granitic Rocks Northgate District Colorado
    Metamorphism and the Origin of Granitic Rocks Northgate District Colorado GEOLOGICAL SURVEY PROFESSIONAL PAPER 274-M Metamorphism and the Origin of Granitic Rocks Northgate District Colorado By T. A. STEVEN SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 274-M A discussion of the progressive metamorphism, granitixation, and local rheomorphism of a layered sequence of rocks, and of the later emplacement and deuteric alteration of an unrelated granitic stock UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1957 UNITED STATES DEPARTMENT OF THE INTERIOR FRED A. SEATON, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. CONTENTS Page Page Abstract_________________________________ 335 Pre-Cambrian geology—Continued Introduction-_______________________________________ 335 Dacite porphyry—____ ——— __ —— _____________ 364 Acknowledgments__ ___--_____-____-_____-______-_ 336 Intrusive quartz monzonite_-____--_-__-_--_-_-_. 365 Geologic setting._______ — _________________________ 336 Petrography ________—— —— _______________ 365 Pre-Cambrian geology—___________________________ 337 Main body of the stock____________— 366 Hornblende gneiss___-_________-_-_____-________ 338 Marginal dikes_________-____-__-__——— 366 Quartz monzonite gneiss_________________________ 342 Satellitic dikes___-___.__________ 367 Biotite-garnet gneiss___________________________ 345 Wall-rock alteration_________ _ __——_ 368 Pegmatite_________________________________
    [Show full text]
  • Magnesio-Hornblende Ca2[(Mg,Fe2+)4Al]
    2+ Magnesio-hornblende Ca2[(Mg; Fe )4Al](Si7Al)O22(OH)2 c 2001 Mineral Data Publishing, version 1.2 ° Crystal Data: Monoclinic. Point Group: 2=m: As prismatic crystals; as reaction rims on pyroxenes. Twinning: Simple or lamellar twinning 100 . k f g Physical Properties: Cleavage: Perfect on 110 , intersecting at 56 and 124 ; partings on f g ± ± 100 , 010 . Tenacity: [Brittle.] Hardness = [5{6] D(meas.) = 3.10{3.28 D(calc.) = 3.26 f g f g Optical Properties: Semitransparent. Color: Green, brown. Luster: [Vitreous to pearly.] Optical Class: Biaxial ({). Pleochroism: X = yellow; Y = Z = green. Orientation: Y = b; Z c = 15 {19 . ® = 1.675 ¯ = 1.690 ° = 1.695 2V(meas.) = 56 ^ ± ± ± Cell Data: Space Group: C2=m: a = 9.887(2) b = 18.174(5) c = 5.308(5) ¯ = 104± 58(2)0 Z = 2 X-ray Powder Pattern: Sierra Nevada batholith, California, USA. 3.136 (100), 8.51 (56), 2.720 (33), 3.291 (26), 2.818 (19), 2.172 (19), 1.656 (18) Chemistry: (1) (2) (1) (2) SiO2 48.20 44.12 Na2O 1.96 1.18 TiO2 1.00 1.26 K2O 0.41 0.88 Al2O3 10.00 8.82 F 0.14 Fe2O3 3.50 5.53 Cl 0.07 + FeO 10.60 14.77 H2O 2.22 1.80 MnO 0.17 0.50 H2O¡ 0.45 0.00 MgO 10.06 9.19 O = (F; Cl) 0.08 ¡ 2 CaO 10.59 11.74 Total 99.16 99.92 2+ (1) Sibukawa district, central Japan; corresponds to (Ca1:66Na0:55K0:08)§=2:29(Mg2:18Fe1:29 3+ Fe0:39Al0:76Ti0:10Mn0:02)§=4:74(Si7:04Al0:96)§=8:00[O21:84(OH)0:16]§=22:00(OH)2:00: (2) Sierra 2+ Nevada batholith, California, USA; corresponds to (Ca1:90Na0:35K0:17)§=2:42(Mg2:07Fe1:86 3+ Fe0:63Al0:23Ti0:14Mn0:06)§=4:99(Si6:66Al1:34)§=8:00O22[(OH)1:87F0:07Cl0:02]§=1:96: Polymorphism & Series: Forms a series with ferrohornblende.
    [Show full text]